The expiration of a temporary break in Social Security withholdings means paychecks have shrunk, which experts say could have a chilling effect on consumer spending.

In the debate over the “fiscal cliff,” Congress allowed the cut to expire, causing Social Security taxes to return to 6.2 percent from the 4.2 percent Americans were paying over the past two years.

The expiration of the tax break means the average household will have $18 to $20 less each week, or $900 to $1,000 less each year, said Roberton Williams, a tax economist and the Sol Price Fellow at the Tax Policy Center in Washington.

That represents a total decrease for U.S. consumers of $120 billion from last year, or roughly 0.8 percent of U.S. gross domestic product.

“It’s like getting a pay cut,” said Michael Goodman, an economic analyst and chairman of the department of public policy at the University of Massachusetts at Dartmouth. “We do use those payroll taxes to fund Social Security and Medicare, but there’s an economic price to be paid.”

Fred Breimyer of the New England Economic Partnership said that it could affect consumer confidence.

“This is a very unsettled time,” Breimyer said. “People are concerned about their well-being. It’s going to make a difference to disposable income.”

Sales by Massachusetts retailers grew by 2.76 percent in November and December, just above the national average of 2.5 percent over the same period in 2011. But the expiration of the payroll tax cut could reduce those gains, said Christopher Geehern, executive vice president of the Associated Industries of Massachusetts.

“It makes people less likely to have a meal out or purchase things,” Geehern said.

“Any loss of consumers’ spending or buying power means retailers will take a hit,” said Bill Rennie, vice president of the Retailers Association of Massachusetts. “For us, it’s all about consumer confidence. If people see a decrease in their take-home pay and they start to pull back, our members will feel it.”

Retailers in the Bay State also will be impacted by whether the Legislature passes Gov. Deval Patrick’s combination of sales tax cuts and income tax increases to fund transportation and education.

The extent to which the Social Security tax bump impacts consumer spending depends on whether wages start to increase after stagnating for the last few years, said Andre Mayer, senior vice president for research at the Associated Industries of Massachusetts.

“It’s an almost subliminal effect,” Mayer said. “If people’s pay was rising, they probably wouldn’t notice at all. But wages really have not been going up. So if the idea of the tax cut was that having a little more money in people’s paychecks would make them spend more, then having a little less now presumably will make them spend less.”